Mathematic Article - Tests of primalidad
A list of simple rules to consider of tests of divisibilidad that will help us to verify the primalidad of a number. A natural number is divisible by :
* 2: If the number is even
* 3: If the sum of its digits is divisible by 3
* 4: If both last digits are a divisible number by 4
* 5: If the last digit is 5 or 0
* 6: If the number is even and divisible by 3
* 7: S.A. to suppress the number of the units and to reduce of the number that is left the double of the suppressed number is left a number multiple of 7
* 8: If the number is divisible by 4 and the result is even
* 9: If the sum of its digits is divisible by 9
* 10: If the last digit is 0
* 11: If the absolute value of the difference between the sum of the numbers that occupy even place and the sum of the numbers of uneven place
Check Here for test result : http://www.mste.uiuc.edu/html.f/resource/prime.html
The problem is from 10… Some truquillo: P? (Safe, as in the case of the 7, to know a little memory the multiples of he himself)
He is divisible by 7: when when suppressing the number of the units and reducing of the number that is left the double of the suppressed number is left a number multiple of 7
He is divisible by 11: when the absolute value of the difference between the sum of the numbers that occupy even place and the sum of the numbers of uneven place.
Example: 1384856 are divisible between 11 then
1+8+8+8=23
3+4+5=12 23-12=11
I hope it to have explained well.
If we put purists,
7: S.A. to suppress the number of the units and to reduce of the number that is left the double of the suppressed number “and to take its absolute value” is left a number multiple of 7 or 0.
(In the first cases it gives -7 and 0 for some numbers)
11: If the absolute value of the difference between the sum of the numbers that occupy even place and the sum of the numbers of 11 uneven place “is or multiple of 11.”
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